Peening Device for Peening Welds Inside Steel Submarine Pipes, Process for Producing Steel Submarine Pipes Using Such a Device, and Submarine Connection Pipe

ABSTRACT

A peening device suitable for peening annular weld zones inside undersea pipes, the device comprising at least one peening tool, with at least one hammer actuated to perform radial reciprocating movement in translation for peening against the inside surface of the pipe and/or said weld, wherein:
         said peening tool has a single hammer; and   said hammer is pivotally mounted so as to be capable of varying its angle of inclination relative to the surface for peening; and   said device includes a carriage suitable for moving in axial longitudinal translation XX inside a pipe and for supporting means for moving said peening tool in longitudinal and radial translation, and in rotation relative to said carriage; and   said hammer co-operates with means for actuating radial reciprocating movements in translation by peening by making use of electromagnetic energy and reciprocating motion inside a solenoid coil, preferably also in co-operation with a spring.

The present invention relates to a method of treating welds in a steel pipe, in particular an undersea pipe for conveying corrosive fluids, and in particular water, the method comprising assembling unit pipe elements together by welding.

The present invention relates more particularly to a subsurface connection installation between a floating support and an oil loading buoy.

The present invention relates more particularly to a bottom-to-surface connection installation comprising at least one undersea pipe providing a connection between a floating support and the bottom of the sea, in particular at great depth. Such undersea pipes are referred to as “risers” and they are made up of unit tubular elements made of steel that are welded together end-to-end.

More particularly, the present invention provides a riser type undersea pipe for making a connection between a floating support and the bottom of the sea, said riser being constituted by a rigid, catenary-type pipe that extends from said floating support to a point of contact with the sea bottom.

The technical field of the invention is thus the field of fabricating and installing undersea pipes and more particularly production bottom-to-surface connections for offshore extraction of oil, gas, or other soluble or phase-change material, or a suspension of mineral material, from an undersea well head in order to develop production fields located at sea or off-shore. The main and immediate application of the invention lies in the field of oil production, and also in reinjecting water and producing or reinjecting gas.

In general, a floating support includes anchor means enabling it to remain in position in spite of the effects of currents, winds, and swell. It also generally includes means for drilling, storing, and processing oil, and means for off-loading to off-loading tankers that call at regular intervals to remove production. Such floating supports are referred to as floating production storage off-loading (FPSO) vessels or as “floating drilling and production units” (FPDU) when the floating support is also used for performing drilling operations with wells being deflected in the depth of the water.

An undersea pipe or “riser” of the invention may constitute either a “production pipe” for crude oil or gas, or a water injection pipe providing a connection with an undersea well head at the sea bottom, or indeed a “drilling riser” providing the connection between the floating support and a well head located on the sea bottom.

A multiplicity of lines are generally installed on FPSOs and it is necessary to implement either hybrid-tower type bottom-to-surface connections or else catenary type connections, i.e. connections that follow a catenary curve.

When the bottom-to-surface connection pipe is of the catenary type, it provides a direct connection between a floating support and a point of contact with the sea bottom that is offset from the axis of said support, said pipe taking up a so-called “catenary” configuration under the effect of its own weight, i.e. a curve having a radius of curvature that decreases from the surface down to the point of contact with the sea bottom, with the axis of said pipe forming an angle α relative to the vertical that varies in general from 10° to 20° at the level of the floating support up to, theoretically, 90° at the sea bottom corresponding to a theoretical position that is substantially tangential to the horizontal, as explained below.

Catenary type connections are generally made with the help of flexible pipes, however they are extremely expensive because of the complex structure of the pipe.

As a result, substantially vertical risers have been developed so as to bring the catenary-configuration flexible connection closer to the surface near the floating support, thus making it possible to minimize the length of said flexible pipe, and also to minimize the forces that are applied thereto, thereby considerably reducing its cost.

Once the depth of water reaches or exceeds 800 meters (m) to 1000 m, it becomes possible to make said bottom-to-surface connection with the help of a thick-walled rigid pipe since the considerable length of the pipe presents sufficient flexibility to obtain a satisfactory catenary configuration while remaining within acceptable stress limits.

Such rigid risers of thick strong materials in a catenary configuration are commonly referred to as steel catenary risers (SCRs) regardless of whether they are made of steel or of some other material such as a composite material.

Such “SCRs” are much simpler to make than flexible pipes and therefore much less expensive.

The geometrical curve formed by a pipe of uniform weight in suspension and subjected to gravity, known as a “catenary”, is a mathematical function of the hyperbolic cosine type (Cosh(x)=(e^(x)+e^(−x))/2), relating the abscissa and the ordinate of an arbitrary point on the curve in application of the following formulae:

y=R ₀(cosh(x/R ₀)−1)

R=R ₀(Y/R ₀+1)²

in which:

-   -   x is the distance in the horizontal direction between the point         of contact and a point M on the curve;     -   y represents the altitude of point M (x and y are thus the         abscissa and the ordinate of a point M on the curve relative to         an orthogonal frame of reference having its origin at said point         of contact);     -   R₀ is the radius of curvature at said point of contact, i.e. the         point where the tangent is horizontal; and     -   R is the radius of curvature at the point M (x,y).

Thus, curvature varies along the catenary from the surface where its radius of curvature has a maximum value R_(max) down to the point of contact where its radius of curvature has a minimum value R_(min) (or R₀ in the above formula). Under the effect of waves, wind, and current, the surface support moves laterally and vertically, thereby having the effect of raising and lowering the catenary-shaped pipe in the vicinity of the sea bottom.

Thus, the pipe presents a radius of curvature that is greatest at the top of the catenary, and in generally at least 1500 m, and in particular lies in the range 1500 m to 5000 m, i.e. at the point where it suspended from the FPSO, with said radius of curvature decreasing down to the point of contact with the bottom. At that location, the radius of curvature is at a minimum in the portion that is suspended. However, in the adjacent portion that is resting on the sea bottom, said pipe is theoretically in a straight line so its radius of curvature is theoretically infinite. In fact, since some residual curvature remains, said radius is not infinite, but it is extremely large.

Thus, as the floating support moves on the surface, the point of contact moves forwards and backwards, and in the zone that is lifted from or lowered onto the bottom, the radius of curvature passes in succession from a minimum value R_(min) to a value that is extremely large, or even infinite in a theoretical configuration where the undersea pipe rests on the sea bottom substantially in a straight line.

This alternating flexing gives rise to fatigue phenomena that are concentrated throughout the foot zone of the catenary, and as a result the lifetime of such a pipe is greatly reduced and in general not compatible with the lifetimes desired for bottom-to-surface connections, i.e. 20 to 25 years, or even more.

In addition, during these alternating movements of the point of contact, it is observed that the stiffness of the pipe associated with the above-mentioned residual curvature acts over time to dig a furrow over the entire length that is raised and then lowered back down again, so as to create a transition zone in which there exists a point of inflection where the radius of curvature, which is at a minimum at the foot of the catenary, changes direction in said transition zone and increases finally to reach an infinite value in a portion of undersea pipe that is resting in a straight line on the sea bottom.

These repeated movements over long periods dig a furrow of considerable depth in bottoms that are poorly consolidated, as are commonly to be found at great depths, thereby having the effects of modifying the curvature of the catenary and, if the phenomenon becomes amplified, of leading to risks of damage to the pipes, or to other undersea pipes lying on the sea bottom, or to the SCRs that provide connections between said undersea pipes resting on the sea bottom and the surface.

These pipes are made by welding unit pipe elements together end-to-end. The unit pipe elements are themselves assembled to form strings, in general strings of two to four unit elements welded end-to-end, which strings are then taken to sea. In known manner, these strings are assembled by being welded to one another at sea from a pipe-laying ship, in particular in a J-lay tower. The assembly welds are made preferably and for the most part from the outside of the pipe.

The most critical portion of a riser is situated at the assembly welds between unit pipe elements, in particular in the portion of the riser that is closest to the point of contact, and the major fraction of the forces in this low portion of the catenary are generated by the movements of the floating support and by the excitations that are applied to the top portion of the catenary, which is subjected to current and swell, with all of these excitations then propagating mechanically along the entire length of the pipe to the foot of the catenary.

The steels from which pipes are made are selected to withstand fatigue throughout the lifetime of installations, however, the welds between pipe elements, in this catenary foot zone constitute weak points when said pipe conveys water or fluid that includes water, and more particularly salt water. In the presence of water, said welds are subjected to fatigue and corrosion phenomena that give rise over time, and under varying bending stresses, to cracks that lead to said pipes being destroyed.

To mitigate that problem, welds are made between pipe elements using a stainless steel or an alloy that withstands corrosion. Anti-corrosion alloys are well known to the person skilled in the art, and are constituted mainly by nickel-based alloys, in particular of the Inconel type, preferably of a specific grade, and in particular Inconel 625 or 825. Such Inconels also present excellent resistance to fatigue as a result of their high elastic limits, thereby making it possible to achieve lifetimes of 20 to 30 years.

In order to enable the welds to be strong and to be made under good conditions, proposals have been made to line the insides of two pipe elements for welding together with the same stainless steel or corrosion-resistant alloy over a length of a few centimeters in the vicinity of each end of the pipe elements for welding together, so that the penetration pass of the weld that constitutes the future wall in contact with the fluid is of the same metal as the welding filler metal, and in particular Inconel. Such a lining of stainless steel or anti-corrosion alloy, in particular of the Inconel type, is provided using an expensive arc method referred to as “cladding”, and generally performed using a tungsten inert gas (TIG) method or a plasma method, associated with a filler wire or with a powder of stainless steel or of corrosion-resistant alloy.

The object of the present invention is to provide a novel method of fabricating and installing undersea pipes for conveying corrosive fluids and in particular water, the method comprising welding together undersea pipe strings at sea on board a ship for laying undersea pipes, which method should:

-   -   be reliable in terms of resistance to fatigue at each of the         welds, and in particular avoid cracks appearing over time;     -   have as little effect as possible on the mechanical strength of         the pipe and/or increase as little as possible head losses in         the fluid conveyed inside the pipe when in operation; and     -   be as simple and as inexpensive as possible to implement, in         particular with the assembly steps and in particular the         welding, being performed as little as possible on board the         laying ship.

In the present invention, the inventors have discovered that incipient cracks are located on the inside of the pipe in the vicinity of the small projection of the weld bead that extends towards the inside of the pipe, and not on the outside face comprising the main bulk of the weld bead on the outside of the pipe. More precisely, and as explained in the detailed description below given with reference to FIGS. 3E and 3F, the inventors have discovered that the origin of weld destruction lies in the transition zone between the welds and the inside surface made of the base steel of the adjacent pipe, in which zone traction stresses associated with thermal shocks during welding can give rise to physical defects, and in particular to incipient cracks located in said zone.

During welding, uncontrollable localized quenching or shrinkage occurs, leading to contraction stress states of the metal that are localized in and close to the weld zone, even though the remainder of the adjacent surface of the pipe is either at rest or in compression.

In general, these problems of localized contraction stress in welds are solved by annealing to relax the stress. Other means are known for treating such problems in welds in order to relax traction stress, but they are not compatible with the time constraints and the desired rates of laying at sea. However, in present circumstances, annealing treatments are not possible for the welds made between undersea pipe elements while laying the pipe at sea.

U.S. Pat. No. 4,491,001 discloses a device for peening annular welds inside pipes, the steel or metal alloy weld beads constituting said welds being located on the outside of the pipe, said peening being implemented to increase the compression of the steel or metal in the welds and to eliminate traction stresses. In that document, the peening device has a said peening tool mounted at the end of a shaft passing along said pipe axially. Said shaft is moved in rotation about its own axis about said axial longitudinal axis XX of the pipe by using a system of gearing disposed outside the pipe. Said shaft or said pipe is moved in relative longitudinal translation in the axial direction of the pipe. Said peening tool is thus suitable for moving in relative longitudinal translation XX relative to said pipe and in rotation about said axial longitudinal axis XX of the pipe at the end of said shaft and in the vicinity of said welds. The said peening tool has a plurality of hammers suitable for being moved repeatedly in radial translation in said pipe in order to perform said peening perpendicularly against the inside surface of the pipe for peening in the vicinity of said welds. The various hammers are distributed along the inside circumference of the pipe. Said hammers are actuated simultaneously to move in relative radial translation by a common motor that makes use of pneumatic energy.

That type of peening device performs peening that is random but uniform over the peened zone so as to eliminate the internal projection on the back of the external annular weld bead.

FR-2 791 293 discloses a piezoelectric peening tool and U.S. Pat. No. 3,935,055 discloses a peening tool using pneumatic energy, said tools having multiple independent pins that are projected randomly against a surface for treatment.

The object of the present invention is thus to provide a peening method and device that enables peening to be performed more accurately and under greater control, in particular peening that is differentiated in the transition zone between the weld and the adjacent inside surface of the pipe, without necessarily seeking to eliminate the internal seam on the back of the weld bead.

To do this, the present invention essentially provides a peening device suitable for peening annular weld zones inside undersea pipes, the device comprising at least one peening tool, with at least one hammer actuated to perform radial reciprocating movement in translation for peening against the inside surface of the pipe and/or said weld, the device being characterized in that:

-   -   said peening tool has a single hammer; and     -   said hammer is pivotally mounted so as to be capable of varying         its angle of inclination relative to the surface for peening;         and     -   said device includes a carriage suitable for moving in axial         longitudinal translation XX inside a pipe and for supporting         means for moving said peening tool in longitudinal and radial         translation, and in rotation relative to said carriage; and     -   said hammer co-operates with means for actuating radial         reciprocating movements in translation by peening by making use         of electromagnetic energy and reciprocating motion inside a         solenoid coil, preferably also in co-operation with a spring.

More precisely, the present invention provides a peening device suitable for peening the insides of undersea pipes made of steel assembled by annular welding of abutting ends of unitary pipe elements, the weld beads being made from the outside of the pipe, said device comprising at least one peening tool suitable for moving in longitudinal axial translation XX in the axial direction of the pipe, and in rotation about said axial longitudinal axis XX of the pipe in the vicinity of said welds inside the pipe, said peening device having at least one hammer comprising:

-   -   a main body constituting a flyweight of elongate shape in a         longitudinal direction Y1Y1 for reciprocating movement in         translation of said hammer relative to the peening tool and         relative to the inside surface of the pipe or the weld for         peening; and     -   a rounded element of curvature of convex shape at the end of         said flyweight and secured thereto, said rounded element being         suitable for coming into contact with said surface for peening,         thereby creating impacts in the form of craters under the effect         of the kinetic energy of said hammer, when it is actuated for         peening by performing said relative radial reciprocating         movements in translation;

the device being characterized in that:

a) said peening tool has a single hammer; and

b) said hammer is pivotally mounted so as to be capable of varying the angle of inclination of said elongate flyweight and of varying said direction Y1Y1 of relative reciprocating movement in translation of said hammer relative to the radial direction; and

c) said device comprises:

-   -   a first carriage suitable for moving in axial longitudinal         translation XX inside a pipe; and     -   said first carriage supporting means for moving said peening         tool in relative axial longitudinal translation XX relative to         said first carriage, in particular in such a manner that said         peening tool can perform peening of said weld zone and on either         side thereof over a distance L for peening, in said longitudinal         axial direction XX astride said weld, that is not less than the         width of the weld plus 1 millimeter (mm), to 10 mm on either         side thereof; and     -   said first carriage supporting means for implementing relative         rotation of said peening tool relative to said first carriage         about said axial longitudinal axis XX of the pipe, in particular         at said welds (6), thus enabling said peening to be performed         over the entire circumference of the inside surface of said pipe         by performing a said rotation of the peening tool (5); and     -   said first carriage supporting means for moving said peening         tool in said relative radial reciprocating movement YY relative         to said first carriage, making it possible in particular to         cause said peening tool (5) to approach the inside surface of         the pipe, or to cause the peening tool (5) to move away from the         inside surface of the pipe; and

d) said peening tool includes means for actuating peening by said radial reciprocating movement in translation by implementing electromagnetic energy, the hammer comprising a said main body made of magnetic material suitable for reciprocating in both directions inside a stationary solenoid coil along the axial direction of said solenoid corresponding to said longitudinal direction Y1Y1 of said hammer under the effect of a magnetic field created inside the solenoid when said solenoid is powered with direct current (DC) alternately in both directions, said main body also preferably co-operating with a spring.

The term “reciprocating radial movement in translation” is used to mean repeated back-and-forth movements in translation in succession against the inside surface of the pipe so as to create a plurality of impacts, preferably in the form of adjacent craters covering the entire peened surface.

This type of solenoid electromagnetic motor is known to the person skilled in the art as a “linear motor”, in particular for loudspeaker coils (“voice coil motors”) that operate in similar manner but generally inversely, i.e. it is the coil that moves while the magnet bar remains stationary.

When implementing electromagnetic actuation in this way, said main body is preferably made of ferromagnetic steel, or of magnetic alloy, in particular a samarium-cobalt alloy or a neodymium-boron alloy.

In a preferred embodiment, the electrical power supply to the solenoid is controlled under digital control as a function of the position of the hammer that is determined using a sensor, thereby making it possible to adapt the peening energy, i.e. the energy that is transferred by the hammer to the surface being treated.

It is thus possible to transfer substantially constant amounts of energy over the entire surface for treatment.

Advantageously, the peening device of the present invention includes the following characteristics:

-   -   said first carriage is motor driven and supports a first shaft         disposed inside the pipe in said axial longitudinal direction XX         of the pipe; and     -   said first shaft supports at least transverse guidance support         or means preferably in the form of a beam, suitable for guiding         the movement of at least one second carriage in radial         translation in a transverse direction perpendicular to said         axial longitudinal direction XX, said second carriage supporting         said peening tool and said second carriage preferably including         means suitable for maintaining said peening tool in a position         facing the inside surface of said pipe; and     -   said first shaft includes drive means for causing it to perform         controlled rotation about its own said axial longitudinal axis         XX so as to be capable of moving said radial transverse guide         support and said peening tool in relative rotation over the         entire circumference of the inside surface of the pipe; and     -   said first shaft is preferably suitable for being driven in         relative translation relative to said first carriage in said         axial longitudinal direction XX of the pipe, at least over a         said limited distance L.

Also advantageously, said first carriage is driven by a motor powered from outside the pipe by an umbilical connection, and said first carriage has wheels pressed against the inside surface of the pipe and guiding said axial longitudinal movement in translation of said first carriage inside the pipe, said wheels being connected to an axial main body of the first carriage by a system of arms mounted as hinged parallelograms.

Still more particularly, said system of arms mounted as hinged parallelograms comprises three parallelogram structures, each carrying two wheels in alignment on the axial direction XX of the pipe, the three parallelogram structures preferably being distributed uniformly at 120° from one another, and being actuated synchronously by springs or actuators so that the main body of said first carriage remains substantially on the axis XX of said pipe.

Advantageously, said rounded element of convex curvature of said hammer defines a body of revolution of spherical, oval, or parabolic shape, preferably of spherical shape, made of a steel or a metallic carbide of hardness that is greater than that of said main body of the hammer, and said convex element presents a small dimension in cross-section, in particular a small diameter, compared with the corresponding dimension of the main body, in particular the cross-sectional diameter of said main body of the hammer.

More particularly, said convex element terminating the hammer presents hardness on the Vickers scale greater than 500 HV, and preferably greater than 750 HV.

The main body presents dimensions in length and in cross-section that are sufficient, and thus a mass that is sufficient, to confer a large amount of kinetic energy to the hammer, while the small dimension of the cross-section of the convex terminal element and its greater hardness seeks to concentrate said kinetic energy at the point of impact with the surface for treatment over a small area, said great hardness of the terminal element thus avoiding any permanent deformation of said terminal element.

Preferably, said convex terminal element is made of tungsten carbide. It is also possible to use a said terminal convex element that is made of tempered steel of the type used for ball bearing balls. In any event, the main body is made of magnetic material, either in part only or completely.

Advantageously, the device has a plurality of peening tools, each having a single said hammer, each peening tool being suitable for being moved independently, and each hammer being suitable for controlled to perform peening independently.

More particularly, the device has two peening tools, said first shaft supporting two said second carriages each supporting one said peening tool on a common said transverse guidance support.

Still more particularly, the device of the invention has four peening tools, said first shaft supporting two said transverse guidance supports offset in the longitudinal and rotary directions, each of said guidance supports being suitable for guiding the movement of two said second carriages in radial translation, each carriage supporting a single said peening tool.

The present invention provides a method of treating welds in a steel pipe assembled by welding together the abutting ends of unit pipe elements, the steel or metal alloy weld beads of said welds being located on the outside of the pipe, the method being characterized in that localized peening is performed inside the pipe to increase the compression of the steel or the metal in said welds and over the adjacent peripheral inside surface of the pipe on either side of the welds so as to create a peened surface swath over a distance L that is limited in the axial longitudinal direction of said pipe, preferably over a distance L that is greater than the width of the weld inside the pipe, preferably over a distance L that is not less than the width of the weld inside the pipe plus a width of 1 mm to 10 mm on either side thereof, said peening being performed by creating a plurality of impacts using a peening device of the invention having at least one peening tool with a single tiltable hammer that is driven by an electromagnetic motor on a self-propelled movable carriage as defined above.

Preferably, the weld comprises a main weld bead outside the pipe and a projection or internal seam of smaller thickness projecting from the inside of the pipe, and said peening is performed at least in the transition zone between the inside surface of said seam at the back of the weld bead and the adjacent inside surface of the pipe, by varying the angle of inclination β of the longitudinal direction Y1Y1 of movement in translation of said hammer relative to said direction YY of movement in radial translation of said second carriage.

More particularly, said peening is performed in such a manner as to establish compression or increase compression over a thickness of 0.2 mm to 2 mm in said inside surface of the pipe and of said weld.

In an implementation, the limited distance L represents one to three times the thickness of the pipe.

Still more particularly, peening is performed in such a manner so as to obtain compression stress greater that 5 megapascals (MPa), preferably greater than 50 MPa, and in particular lying in the range 50 MPa to 1000 MPa, over the entire peened surface.

More particularly, said peened swath extends over a distance L that is not less than half the thickness of the pipe wall, and more preferably over a distance L that is less than twice the thickness of the pipe.

More particularly, the weld comprises a main weld bead on the outside of the pipe and a projection or seam on the inside that is of smaller thickness and that projects into the inside of the pipe. This internal projection or seam results from the partial melting of the ends of the unit elements that are assembled together by welding, said melting taking place during the welding heat treatment.

More particularly, said peened swath extends over a distance L corresponding to the width of the weld on the inside of the pipe, in particular the width of said internal seam, which seam presents a width lying in practice in the range 3 millimeters (mm) to 5 mm, plus a width on either side lying in the range 1 mm to 10 mm, so as to give a distance L lying in the range 5 mm to 25 mm.

The term “peening” is used herein to mean surface treatment by multiple impacts using one said hammer so as to increase the level of compression stress in a zone of the surface under treatment.

According to the present invention, it is the entire surface of said swath, i.e. the cylindrical inside surface section on either side of the weld, overlapping the weld, that is subjected to these impacts, with no zone of the surface outside said swath needing to subjected to such an impact.

When the rounded element of convex curvature at the end of the hammer strikes the surface for treatment during an impact, part of its kinetic energy is transformed into plastic and elastic deformation energy in the surface being treated, thereby having the effect of creating localized cold forging, and thus of increasing the compression stress in the material where it is treated, and as a result eliminating residual zones of traction stress. A small crater is created in the peened surface with plastic deformation of the steel of the pipe being greater in the center of said crater relative to its periphery.

Peening in the present invention consists, so to speak, in cold forging to eliminate residual traction stresses by deforming the material in the peened surface. It should be observed that it is not desired to eliminate any extra thickness associated with an inside seam or projection of the weld bead, but only to apply compression in substantially uniform manner to the surface of the welding zone and of the adjacent zones, using sufficient energy to plasticize and deform the metal so as to eliminate any residual traction stresses due to the welding operation.

Still more particularly, said ends of the unit pipe elements for welding together comprise, in longitudinal axial section, a straight end beside the inside of the pipe forming a root face that preferably occupies at least one-fourth of the thickness of the main portion of the pipe and that is extended towards the outside of the pipe by a sloping chamfer.

Under such circumstances, the inside projection or seam of the weld that stands proud is a made up molten metal from said root face and of the filler metal.

It will be understood that said chamfer faces towards the outside of the pipe so that it can receive a weld bead deposited between the two chamfers at the ends of two abutting pipe elements, thereby substantially forming a V-shape at the end of the two pipe elements for butt welding together.

In an advantageous implementation, material is removed by prior grinding or by milling, from the inside surface of the pipe and from the weld bead over the surface that is to be peened, prior to said peening, with a rotary grinder tool mounted in the place of said peening tool on a said first carriage.

Still more particularly, the method of the invention is characterized in that it includes the following steps:

-   -   said first carriage is moved in translation inside said pipe in         said longitudinal axial direction XX, such that said peening         tool is substantially positioned so as to be capable of         performing peening in said weld zone and on either side thereof         over a said distance L for peening astride said weld in said         longitudinal axial direction XX; then     -   said peening tool is moved against or close to the inside         surface of the pipe by moving said peening tool in radial         translation YY; then     -   said peening tool is then moved in rotation about said axial         longitudinal axis XX over the circumference of the inside         surface of the pipe; and then     -   where appropriate, the peening tool is moved in relative         translation in the axial longitudinal direction XX relative to         said first carriage so as to perform the peening and compression         over the entire peened surface.

It will be understood that the longitudinal movement of the peening tool in translation relative to said first carriage may be performed either continuously, or else essentially between two of said rotations of said peening tool. This makes it possible to avoid leaving any non-peened area between two impact zones of said successive projectiles, and thus to reach the most critical zones that are situated at the interface between the seam of the weld bead and the base metal of the pipe.

More particularly, said welding is performed using carbon steel, stainless steel, or a corrosion-resisting alloy of the Inconel type having high elasticity, and good fatigue resistance, and preferably Inconel of grade 625 or 825.

Still more particularly, the method of the invention comprises the following successive steps:

1) in a workshop on land, assembling the respective ends of at least two unit pipe elements together end-to-end by said welding in order to form pipe strings; and

2) at sea, on board a laying ship fitted with a J-lay tower, assembling respective ends of said strings together by said welding to form a pipe.

The present invention also provides a bottom-to-surface connection undersea pipe having at least a portion including zones of said assembly welds between unit pipe elements that have been put into compression by differentiated peening of said transition zone using a said inclined hammer in a method of the invention.

More particularly, the present invention provides a bottom-to-surface connection undersea pipe of the invention that is characterized in that it is a catenary pipe of the SCR type with at least a portion thereof, including the zone that comes into contact with the bottom and extending from the bottom over at least 100 m, and preferably 200 m, being assembled by a pipe-making method of the invention.

Other characteristics and advantages of the present invention appear in the detailed light of embodiments described below with reference to the accompanying figures, in which:

FIG. 1 is a side view of a pipe in a simple catenary configuration 1, suspended from a floating support 10 of the FPSO type, having its bottom end resting on the sea bottom 13, and shown in three different positions 1 a, 1 b, and 1 c;

FIG. 1A is a side view in section showing in detail the trench 12 that is dug by the foot 11 of the catenary during movements in which the pipe is lifted off and rested on the sea bottom;

FIG. 2 is a longitudinal section of a pipe and a side view of a peening robot 3 inside the pipe while it is being assembled, shown during peening treatment of the weld 6 between the ends of two pipe elements 2 a and 2 b, the weld being shown in the bottom half only of the section;

FIG. 2A is a section view of the pipe showing the peening robot 3 inside the pipe;

FIG. 3 is a longitudinal section view of one end of a pipe element showing a straight portion (root face) and an inclined portion (chamfer);

FIGS. 3A, 3B, 3C, and 3D are side views in section showing all or part of the respective ends of two pipe elements to be assembled together, respectively during an approach and positioning stage (3A), a welding stage (3B), an internal grinding stage (3C), and a peening stage (3D). FIGS. 3C and 3D show only a bottom portion of the weld so as to show more clearly the inside surface 6 ₃ of the weld bead 6 after it has been ground;

FIG. 3A′ shows a variant of FIG. 3A in the event of a small offset between the end root faces of two pipe elements for assembling together;

FIGS. 3B′ and 3C′ are fragmentary longitudinal sections corresponding to FIGS. 33 and 3C and showing only the bottom portion of the weld and of the pipe;

FIGS. 3E and 3F show variants of FIGS. 3B′ in the event that the pipe ends are offset, as in FIG. 3A′, with a incipient crack from the inside being shown at 2 k in FIG. 3F;

FIG. 4A shows a pipe-laying ship fitted with a J-lay tower;

FIG. 4B is a side view of a pipe 2P being lowered down to the sea bottom and held under tension within said J-lay tower, and a string 2N held in the top portion of said J-lay tower, said string being approached to said suspended pipe 2P for the purpose of being assembled thereto by welding;

FIG. 4C is a side view in section showing the two ends of the pipe elements, in the bottom portion of the figure peening has not yet been performed at 7 ₂, while said peening is taking place in the top half-portion at 7 ₁;

FIG. 4D is a side view showing a string 2 made up of four pipe elements 2 a-2 d assembled to one another and ready for transferring to the J-lay ship of FIG. 4A;

FIGS. 5A and 5B are a side view of a peening tool 5 having a single hammer associated with control electronics, the hammer being shown respectively in a deployed position (FIG. 5A) and a retracted position (FIG. 5B);

FIGS. 5C and 5D are side views in longitudinal section on the axis Y1Y1 of the hammer, showing variant hammers in which the percussion ends present respectively parabolic curvature with a small radius of curvature (FIG. 5C), and spherical curvature with a relatively larger radius of curvature (FIG. 5D);

FIG. 5E is a side view of a tiltable peening tool having a single hammer;

FIG. 6 is a detail view of a grinder tool 19 mounted on a said second carriage 4 c, taking the place of the peening tool 5.

FIG. 7 is a side view of a robot 3 fitted with two peening tools 5; and

FIG. 7A is a face view showing the end of a robot 3 fitted with a turntable carrying four peening tools arranged diametrically opposite one another in pairs.

In FIG. 1, there can be seen a side view of a bottom-to-surface connection 1, 1 a, 1 b, and 1 c of the SCR type, that is suspended from a floating support 10 of the FPSO type anchored at 15, the pipe resting on the sea bottom 13 at its point of contact 14 a, 14 b, 14 c.

Curvature varies along the catenary from the surface, where the radius of curvature has a maximum value, to the point of contact where the radius of curvature has a minimum value R₀, R₁, R₂. Under the effect of waves, wind, and current, the floating support 10 moves, e.g. from left to right as shown in the figure, thereby having the effect of lifting or lowering the catenary-shaped pipe off or onto the sea bottom. In position 10 c, the floating support is away from its normal position 10 a, thereby having the effect of tensioning the catenary 1 c and raising it, thereby moving the point of contact 14 towards the right from 14 a to 14 c; the radius of curvature at the foot of the catenary increases from R₀ to R₂, and the horizontal tension in the pipe generated at said point of contact also increases, and consequently the tension increases in the pipe and said floating support. In similar manner, when in position 10 b, the movement to the right of the floating support has the effect of relaxing the catenary 1 b and of resting a portion of pipe on the sea bottom. The radius R₀ at the point of contact 14 a decreases to a value R₁, and similarly the horizontal tension in the pipe at the same time also decreases, as does the tension in the pipe at said floating support. This reduction in the radius of curvature at 14 b gives rise to considerable internal stresses with the structure of the pipe, thereby generating fatigue phenomena that are cumulative and that can lead to the bottom-to-surface connection being destroyed.

Thus, the pipe presents a radius of curvature that is at its greatest at the top of the catenary, i.e. the point where it is suspended from the FPSO, and that decreases down to the point of contact 14 with the bottom 13. At this location, the radius of curvature at the suspended portion is at its smallest, however in the adjacent portion that is resting on the sea bottom, and assuming that said pipe is extending in a straight line, its radius of curvature becomes theoretically infinite. In fact said radius of curvature is not infinite but is very large, since, as a general rule, some residual curvature persists.

Thus, as explained above, as the floating support 10 moves on the surface, the point of contact 14 moves from right to left and in the zone that is lifted off or rested on the bottom, the radius of curvature passes successively from a minimum value R_(min) to a value that is extremely large, or even infinite, in a configuration that extends substantially in a straight line.

This alternating flexing gives rise to fatigue phenomena that are concentrated within the foot zone of the catenary, and the lifetime of such pipes is greatly reduced, and in general is not compatible with the lifetimes that are desired for bottom-to-surface connections, i.e. 20 to 25 years, or even more.

Furthermore, as shown in FIG. 1A, during these alternating movements of the point of contact, it is observed that the stiffness of the pipe, associated with the above-mentioned residual curvature, will over time dig a furrow 12 over the entire length that is raised and lowered, thereby creating a transition zone in which a point of inflection 11 will exist, where the curvature changes direction in the transition zones, so as finally to reach an infinite value in the portion of the undersea pipe that rests in a straight line on the sea bottom, said portion being raised only exceptionally, e.g. in the event of the disturbing elements (swell, wind, current) acting on the floating support and on the catenary all accumulating maximally in the same direction, or else in the event of resonant phenomena appearing in the catenary itself. When the pipe rises, the point of inflection disappears and fibers that were previously in traction are put under compression, thereby creating a considerable amount of fatigue in this portion of pipe. Said fatigue is then one or two orders greater than the fatigue in the main section where no change of curvature occurs, and is incompatible with the looked-for lifetime of 25 to 30 years, or even more.

FIG. 4D shows a string 2 comprising four unit pipe elements 2 a-2 d that are assembled together by welds 2 ₂, 2 ₃, and 2 ₄ made in a workshop. The first end 2 ₁ of said string is for welding to the end 2 ₅ of already-assembled pipe that is being laid, with the end 2 ₅ of the string then constituting the new end 2 ₅ of the pipe being laid and being ready for assembly with the end 2 ₁ of the next string, assembly taking place on board the laying ship 8 shown in FIG. 4A, which ship is fitted with a J-lay tower 9. On board the ship, the strings are stored horizontally on deck, and then they are raised one after another by a pivoting ramp 18 from a horizontal position to a position in which they can be inserted in the J-lay tower 9. The already-laid portion of pipe 2P (not shown in FIG. 4A but visible in FIG. 4B) is held under tension within the tower by means of a clamp. Thereafter, a new string 2N is lowered towards said pipe 2P that is held under tension, as shown in detail in FIG. 4B, and is finally welded thereto, and then subjected to the peening treatment of the invention, as shown in detail in FIG. 4C.

FIG. 2 is a section in side view showing two pipe elements 2 a and 2 b assembled end-to-end by welding 6 in a workshop, the top half-portion being shown in the approach stage prior to welding. Once the welding process has terminated and the weld has been subjected to quality control, a remotely-controlled device or robot 3 is inserted from the right-hand end of the right pipe 2 b, said robot carrying a peening tool 5 of the invention and serving to position said peening tool astride said weld 6, substantially on the axis thereof. The robot 3 serves to enable the inside wall and the weld to be subjected automatically to peening treatment over a swath 7 of width L, e.g. having a total width of 2 centimeters (cm) to 6 cm, i.e. substantially 1 cm to 3 cm on either side of the weld bead 6.

FIG. 3 is a section showing the face of a pipe element that has machined in order to enable it to be assembled to the following element by welding. The face is machined in the plane perpendicular to the axis XX of the pipe and, towards the inside of the pipe, it presents a root face 16 occupying a few millimeters, generally 2 mm to 4 mm, followed by a chamber 17, e.g. a straight and conical chamfer as shown, or a curved and parabolic chamfer (not shown).

In FIG. 3A, two pipe elements have been positioned face to face, ready for welding. When the pipe elements present an extremely high level of quality, or when they have been made so as to present a diameter that is perfectly circular, the inside wall surfaces of said pipe element are substantially continuous. During welding (FIG. 3A, FIGS. 3B-3B′), this gives rise to a small internal projection 6 ₂ that is substantially uniform to the right (2 k) and to the left (2 h) and all around the periphery, as shown in detail in FIG. 3B′.

FIGS. 3E and 3F show the above-described unwanted phenomenon for this type of pipe that is to be subjected to fatigue over a period that may exceed 25 to 30 years. During welding performed from the outside by multi-head orbital welding robots, the first pass needs to merge perfectly with the respective root faces 16 of the two ends of the two pipe elements 2 a and 2 b. For this purpose, the chamfers 17 are prepared as shown in FIGS. 3 and 3A. It is the melting of said root faces that gives rise to a small amount of extra thickness in the form of a narrow seam or projection 6 ₂ (FIG. 3B) towards the inside of the pipe, said extra thickness being substantially rounded but presenting an irregular shape around the periphery of the inside wall of said pipe, and sometimes presenting an angular junction at the interface between the welding and the base metal of the inside surfaces 2 i of the pipe elements.

In general, the pipe elements do not have an internal cross-section that is perfectly circular, with the section being slightly ovalized. Furthermore, wall thickness may vary around the periphery. Thus, when the ends of the two pipe elements for assembling together are placed face to face, although the alignment of FIG. 3A will be found at certain locations of the periphery, there will be other zones where there is an offset, as shown in FIG. 3A′. During the welding process, the projection 6 ₂, which is substantially symmetrical in FIG. 3B′, then presents unbalance, as shown in FIG. 3E. Thus, at 2 h and 2 k respectively identifying the transition zone between the welding itself and the base metal of the pipe elements 2 a and 2 b, there exist respective angles α₁, α₂ between the tangents to the projection and the inside surface 2 i of the pipe, which angles are open to a greater or lesser extent, as shown in FIG. 3E. In general, on the side set back inwards, on the left pipe element 2 a in the drawing, the connection angle α₁ is small, whereas on the other element 2 b, the connection angle α₂ is larger and may result in a sharp angle.

It is then in this zone presenting sharp angles α₂ that there is a risk of generally-localized incipient cracks appearing under the effect of fatigue, which cracks initially propagate in the direction FF as shown in FIG. 3F, and finally propagate around the entire periphery of the pipe, thus leading to destruction of the weld and to destruction of the bottom-to-surface connection.

The welding process involves the use of heating and melting powers, and thus of considerable amounts of energy, since it is desirable to minimize cycle time, particularly for the welding that is performed on board the laying ship 8, as explained above with reference to FIG. 4A to 4D. Such pipe-installing ships have extremely high hourly operating costs, with welding and preparation operations constituting critical busy times. It is desirable to have welding process cycle times of the order of 10 minutes (min) to 12 min for pipes having a diameter of 300 mm and a thickness of 20 mm. The localized thermal shocks created by the power of the welding equipment are considerable and they give rise to residual zones of stress concentration that cannot be treated in conventional manner, in particular by thermal annealing, in order to obtain acceptable relaxation of stresses within a lapse of time that is compatible with the desired rates of laying. Said residual stresses may be compression stresses or traction stresses with traction stresses being more dangerous in terms of fatigue behavior over the lifetime of installations that may exceed 25 to 30 years or more.

During fatigue testing performed on lengths of pipe subjected to fatigue simulations corresponding to that which might be expected over a lifetime of 25 to 50 years, but actually carried out on a fatigue test bench, together with automated frequency spectrum and amplitude for the alternating stress cycles, the inventors have observed localized cracking phenomena at the interface between the base metal of a pipe element and the weld zone, mainly where the root faces 16 melt and at the internal seam 6 ₂ of the weld bead 6. Because of localized quenching phenomena, combined with irregularities in local melting, weak points appear in which the material is in a residual traction stress state to significant level, generally in combination with the presence of a localized physical defect, such as angle. During movement of the pipe, it is specifically at such a location that incipient cracks will appear at 2 _(k), as shown in FIG. 3F, said cracks then propagating rapidly in radial and peripheral manner, in general in a direction FF through the thickness of the wall, thereby leading rapidly to destruction of the pipe and to unacceptable risks of pollution.

The peening device 100 of the invention is constituted by a peening tool 5 supported by a first carriage 3 having wheels 3 e driven by a motor 3 a and powered by an umbilical cord 3 d. The wheels are connected to an axial main body 3 ₁ of the first carriage via a system of arms 3 b mounted as a hinged parallelogram, preferably three parallelogram structures 3 b, each carrying two wheels in alignment on the direction XX. The three parallelogram structures 3 b are preferably uniformly distributed at 120° from one another, as shown in the cross-section of FIG. 2A, and they are actuated synchronously by springs or actuators 3 c so that the main body 3 ₁ of the robot remains substantially on the axis XX of said pipe. The first carriage or robot 3 carries at its front end an axial shaft 4 that is movable in translation along the axis XX in a guide barrel 4 a that is secured to the main body 3 ₁, passing axially therethrough, and movable in translation along said axis XX by an actuator (not shown) that may be a hydraulic cylinder or an electric motor, and that is preferably servo-controlled and operated by a computer via the umbilical cord 3 d. Furthermore, said shaft 4 is capable of rotating about the same axis XX within said guide barrel 4 a. Said rotation of the shaft 4 is actuated by an electric motor (not shown) incorporated in the main body 3 ₁, and preferably controlled and operated by said computer. At the front of the shaft 4, a guide support 4 b secured to said shaft serves to support a second carriage 4 c and guided in a direction perpendicular to the axis XX and to the inside wall 2 i of the pipe 2. Said second carriage 4 c carries a peening tool 5 that is secured thereto. Said peening tool is held in intimate contact with the inside wall 2 i of the pipe 2, preferably with a constant bearing force, e.g. by means of a pneumatic actuator 4 d, with said second carriage 4 c being moved in a transverse direction. Thus, after the weld has been made and inspected, said first carriage or robot 3 is inserted from the right-hand end of the pipe 2 b, carrying the second carriage 4 c that in turn carries the peening tool 5 in a retracted position, thus ensuring that the peening tool does not interfere with the inside surface of the pipe wall. Under drive from the motor 3 a, the robot is moved to the weld 6 for treatment, under monitoring via a video camera 4 e carried by the carriage 4 c. The carriage is then locked in longitudinal position by locking its motor drive 3 a and by increasing the pressure in the actuators 3 c so as to cause the hinged arm 3 b to pivot and jam the wheels 3 a against the inside surface 2 i of the wall of the pipes. The main body is then substantially on the axis XX of the pipe, and the position of the peening tool 5 is adjusted by acting on the position of the shaft 4 that is movable in translation along the axis XX, still under monitoring via the video camera 4 e. The actuator 4 d is then actuated so as to deploy the peening tool in a transverse direction in order to press it against the surface 2 i of the wall of said pipe. The peening tool is then actuated while also driving the shaft 4 in rotation about its axis XX in order to apply said peening tool to the entire periphery of the inner weld bead together with the adjacent internal surfaces 2 i of each of the pipe elements so as to form a peened swath 7 by performing successive circular passes of the peening tool that are slightly offset in longitudinal translation towards the left or towards the right, by modifying the longitudinal position of the shaft 4 that is movable in translation along the axis XX in the guide barrel 4 a secured to the carriage 3.

A peening tool 5 is used that comprises a single hammer 5 ₁ of tempered steel constituted by a main cylindrical body 5 ₅ with a polygonal or circular section of 6 mm to 20 mm and a length of 30 mm to 100 mm, and with a projection at the end of said main body forming an elongate pin, constituted by an element that is extremely hard, e.g. made of fine-grained tungsten carbide, that is of convex shape, defining a parabolic surface of revolution (FIG. 5C) or a spherical surface of revolution (FIG. 5D). For these various shapes of the convex element 5 ₄ in longitudinal section, the element preferably presents a cross-section that is circular and thus creates craters that are substantially circular. The convex element 5 ₄ presents a length along Y1Y1 of 3 mm to 20 mm and a diameter in cross-section of 3 mm to 15 mm. The radius of curvature of the convex element 5 ₄ at its end along the longitudinal axis Y1Y1, i.e. where it comes in contact with the surface being peened, is always less than the radius of curvature of the pipe, but in a preferred version of the invention, it comes as close as possible thereto while in any event being greater than at least half or even two-thirds the radius of curvature of the pipe.

The end of the hammer strikes the surface for treatment, and on impact its kinetic energy is transformed into plastic and elastic deformation energy, thereby creating or increasing the level of compression stress in the material at the point of impact by creating craters that are substantially circular.

In FIGS. 5A-5B and 5E, there can be seen more precisely a carriage 4 c fitted with its peening tool 5 that is remotely controlled via an umbilical connection 5 ₃, the tool comprising a solenoid coil 5 ₆ and a housing 5 ₇ through and in which the main cylindrical body 5 ₅ of a hammer 5 ₁ slides along the axis Y1Y1, said body being made of very high performance magnetic material, e.g. a samarium-cobalt alloy, and it is pre-magnetized so as to present north and south magnetic poles. Such a linear motor is known to the person skilled in the art as a “voice coil motor” and it presents optimum dynamic performance when it is controlled by appropriate electronics, also known to the person skilled in the art. Said control is preferably performed with the position of said hammer as determined by a sensor 5 ₉ being fed back. The solenoid is controlled by an electronics card 5 ₁₀ that is electrically powered at 5 ₁₁, and the position of the hammer is measured in real time by the sensor 5 ₉ as a result of the rod 5 ₁₃ that is secured to the main body 5 ₅ moving, this measurement then being sent 5 ₁₂ to the electronics control card. The hammer 5 ₁ is thus set into reciprocating motion along the direction Y1Y1 as follows: the solenoid is powered with DC so that the main cylindrical body 5 ₅ of the hammer enters into its housing 5 ₇, in which it advantageously compresses a spring 5 ₈ that thus absorbs a fraction of the potential energy. Then, when the hammer is in its high or retracted position, as shown in FIG. 5B, the voltage is reversed, thereby having the effect of subjecting the hammer to a force directed in the opposite direction, i.e. towards the wall of the pipe, with a high level of acceleration under the additional effect of the mechanical potential energy stored in the spring 5 ₈. The hammer thus acquires a high speed and thus a high level of kinetic energy that is transferred to the wall of the pipe as soon as the hammer comes into contact with said wall, thereby performing localized peening of the zone for treatment, as shown in FIG. 5A. The voltage is then once more reversed so as to retract the hammer and perform a new peening cycle, either in exactly the same position, i.e. at the same location, or else in a position that is slightly offset by pivoting the head 4 about the axis XX or by moving it in translation along the direction XX. The reciprocating motion of the hammer is advantageously performed at a frequency of 5 hertz (Hz) to 250 Hz, and in particular 1 Hz to 100 Hz, while advantageously moving the peening tool in regular manner, thereby moving the impact zone both in rotation about the axis XX and in translation along the axis XX, so as to cover in substantially uniform manner all of the swath corresponding to the treated zone 7, so as to obtain a zone that is entirely covered in said adjacent or even overlapping craters.

In a preferred version of the invention, the trajectory of the hammer is controlled in real time by digital control means known to the person skilled in the art. Thus, at each instant, the position of the hammer, its speed, and its acceleration are known and under control, and the energy that is transferred during impact against the wall of the pipe is advantageously maintained stable and repetitive throughout the sequence, the adjustment parameters advantageously be modified depending on the position of the hammer. When the hammer strikes downwards, as shown in FIGS. 5A and 5B the action of gravity on the hammer adds to the acceleration delivered by the control electronics; in contrast, when the hammer is striking the ceiling, i.e. upwards, then the acceleration of gravity is subtracted from the acceleration delivered by the control electronics. The use of a digital control system thus makes it possible, by monitoring the parameters of the hammer trajectory in real time, to transfer a substantially constant level of energy throughout the treatment of the wall, regardless of the orientation of the hammer relative to the vertical.

FIGS. 5C and 5D are side views of the striking end of the hammer either presenting a high degree of parabolic curvature (FIG. 5C), i.e. with a small radius of curvature, or a low degree of spherical curvature (FIG. 5D), i.e. with a radius of curvature that is larger, and that comes close to the internal curvature of the pipe. The diameter and the depth of the zone that is impacted on each stroke of the hammer depends on the energy that is transmitted, on the quality of the base steel of the pipe, on the radius of curvature of said hammer, and on the inside radius of curvature of said pipe.

FIG. 5E shows a peening tool 5 that pivots about the axis 4 f of the support 4 g secured to the carriage 4 c. The axis Y1Y1 of the hammer 5 ₁, which also corresponds to the direction in which said hammer 5 ₁ is projected against the surface for peening, is inclined at an angle β relative to said radial translation direction (YY) of the carriage 4 c, so that it is possible to reach the transition zones 2 h-2 k as described above with reference to FIGS. 3B′ and 3F under the best possible conditions, i.e. the zones that are substantially the closest to a direction perpendicular to the surface of the bead in said zones. This makes it possible to peen with particular insistence on said transition zones 2 h-2 k that are the subject of unwanted cracks appearing. Thus, a first peening tool as described with reference to FIG. 5 is advantageously used for performing general peening. Thereafter, particular insistence is applied to each of the transition zones 2 h-2 k by means of said peening tool 5 being in a position that is inclined at an angle β, e.g. lying in the range 30° to 60°, relative to the direction perpendicular to the inside surface of the pipe, so as to begin by peening the transition zone 2 h, and then subsequently placing said peening tool 5 in a position that is inclined at an angle −β in order to peen the transition zone 2 k. Advantageously, two peening tools 5 are installed on a common carriage 4 c, or on two independent carriages secured to a common axial shaft 4, with one tool being inclined at an angle β and the other tool being inclined at an angle −β.

This peening serves to provide local deformation over a controlled thickness as a function of the energy transmitted by the sonotrode to said needles, the metal of the weld, and the base metal at the end of each of the pipe elements. This plastic deformation of the metal makes it possible to establish a generalized and substantially uniform compression stress state throughout the treated zone 7, thereby having the effect of absorbing any residual localized traction stress state that might result from the welding process and the above-described undesirable localized quenching phenomena.

Achieving compression depends on the power and the accuracy of the peening process, and it is generally performed over a thickness lying in the range 0.2 mm to 2 mm, thereby advantageously preventing unwanted incipient cracks from appearing.

The quality of the pipe in the welding zone is advantageously improved by internally grinding 6 ₃ the weld prior to peening so as to eliminate geometrical surface defects, thereby enabling peening to be performed over an inside surface of the pipe and the welding that is substantially cylindrical where it is peened. Grinding is advantageously performed using a grinder tool 19 as shown in FIG. 6, which tool is mounted on a device similar to said above-described peening tool, but in which the peening tool is replaced with a grinder tool 19. The grinder tool 19 comprises a rotary grindwheel 19 ₁ that is mounted on a said second carriage 4 c and that can therefore be moved in translation in the transverse direction YY such that the rotary grindwheel 19 ₁ comes to bear against the inside surface of the pipe and of the weld for grinding. At least one guide wheel 20 is securely mounted to the grinder tool 19 on one side thereof to serve as a guide to ensure that the rotary grindwheel 19 ₁ is held in position when it comes to bear against said inside surface of the pipe, i.e. so as to ensure that said rotary grindwheel 19 ₁ does indeed remain tangential to the bore of the pipe, and thus removes only the necessary quantity of the projection 6 ₂ of the weld bead 6, as shown in FIGS. 3C-3C′.

FIG. 6 shows a rotary grindwheel 19 ₁ of cylindrical shape and having an axis of rotation X₁X₁, which axis extends in a longitudinal direction parallel to the axial longitudinal direction XX of the pipe, the abrasive surface of the grindwheel corresponding to its cylindrical outer surface. In one embodiment, the cylindrical rotary grindwheel may extend in the direction X₁X₁ over a said distance L. Similarly, the guide wheel 20 presents an axis of rotation X₂X₂ in the longitudinal direction parallel to the axes XX and X₁X₁, such that the guide wheel 20 and the rotary grindwheel 19 ₁ present a common tangent X₃X₃ beside the inside surface 21 of the pipe, thus enabling the guide wheel 20 to guide the grinder tool by maintaining its axis X₁X₁ tangential to the bore 2 i of the pipe, as described above.

FIG. 3D shows the state of the inside surface of the pipe in the peened zone 7 of the inside surface of the weld over a width L.

During prefabrication on land of the strings 2 as shown in FIG. 4D, the length of the unit elements 2 a to 2 d lies in the range about 6 m to 12 m, thereby making it necessary to insert the peening robot from the end that is closest to the weld for treatment, i.e. at a distance of about 6 m to 12 m depending on circumstances, and then cause the robot to travel along said distance in order to take up an accurate position astride said weld for treatment.

During on-site installation, the prefabricated strings generally have a length of about 50 m, as shown in FIG. 4D, or under certain circumstances of 25 m or of 100 m, and it is then necessary to make the robot travel over that distance in order to reach the welding zone for treatment.

FIGS. 4A to 4C show two strings being assembled together together with the welding zone being treated by peening, during on-site installation as performed on board a laying ship 8 that is fitted with a J-lay tower 9, as shown in FIG. 4A. For this purpose, the already-laid pipe element 2P is held securely in suspension from the foot of the tower, and a new pipe element 2N is transferred by means of a pivoting ramp 15 and in known manner from the horizontal position to the oblique position that corresponds to the inclination of the tower, after which it is positioned on the axis of the terminal suspended pipe element. Said pipe element 2N that is to be assembled is subsequently moved axially along the direction XX towards the suspended terminal pipe element 2P, as shown in FIG. 4B, and is then welded thereto in known manner. From the top end of the tower, the peening robot 3 is inserted into the pipe and lowered to the welding zone that is situated 50 m below when using 50 m string, as shown in FIG. 4C, after which a swath 7 is peened in a manner similar to the treatment performed in a workshop and as described above. At the end of treatment, the peening robot is raised back to the top of the tower 9 and then the top end of the pipe is grasped and lowered towards the bottom of the tower so as to be ready to perform a new cycle of assembling and treating a new pipe string.

In the workshop, and on board the installation ship, at the end of the peening treatment of the welding zone, it is advantageous to monitor the state of stresses in the treated zone so as to ensure that traction stress states have been eliminated and replaced by compression stress states. The most appropriate inspection technique is the X-ray method that makes it possible to measure the inter-atomic distances within the surface of the material, and thus to characterize very accurately the stress state and level, regardless of whether stress is in traction, at rest, or in compression. Such means are implemented using a robot similar to that described above, the peening tool 5 being replaced by the X-ray source and the associated sensors that are available from the supplier Stresstech (Finland). The signals recovered by the sensors are then sent to a signal processor unit, e.g. a computer, which deduces therefrom the real stress level that exists after and possibly also before the peening treatment of said welding zone.

The present invention is described mainly for solving the problem associated with bottom-to-surface connections and more particularly in the zone of the point of contact with the sea bottom in an SCR type connection. Nevertheless, the invention applies to any type of undersea pipe, whether it rests on the sea bottom, whether it is incorporated in a vertical tower, or indeed whether it constitutes a subsurface connection between two FPSOs, or between an FPSO and an unloading buoy.

The various types of subsurface connection are described in patent FR 05/04848 in the name of the Applicant, and more particularly in FIGS. 1A-1D and 2A. Said subsurface connections are particularly subject to fatigue phenomena when they are subjected to swell and to currents and above all to the movements of the floating supports, FPSO or loading buoy, which generates alternating stresses, particularly in the zones close to said floating supports.

The peening tool 5 is described in detail above on the basis of an actuator constituted by a linear actuator of the “voice coil motor” type or a linear motor such as the “PowerRod Actuator PRA25” type from the supplier Parker Hannifin GmbH, making it possible to control accurately the amount of kinetic energy that is transmitted to the hammer, and thus the peening energy. The peening tool 5 as described above has only one single hammer, however it is advantageous to juxtapose a plurality of single-hammer peening tools that are independently actuatable, preferably on a common shaft 4, said tools being advantageously distributed regularly around the circumference of the pipe, and optionally being slightly offset relative to one another along the axis XX, so that during rotations of said tools about the axis XX, the zone for treatment 7 is treated in substantially uniform manner in a shorter length of time.

Whatever the inside diameter of the pipe, the energy to be transmitted by the peening tool is substantially the same and depends essentially on the hardness of the metal of the pipe and on the shape of the end of the hammer. The perimeter for treatment is a function of the inside diameter of the pipe, and the treatment time with a single tool therefore increases as a function of said diameter. Thus, for large diameters, it is advantageous to install, preferably distributed in a star configuration around the circumference, a large number of tools that can be actuated independently of one another, e.g. six, 12, or 24 peening tools for pipes having a diameter of 500 mm to 600 mm, since there is sufficient room available for them not to interfere with one another. For small diameters in the range 150 mm to 200 mm, it is possible to install only two or three such peening tools in a star configuration because there is less room available. Advantageously, the majority of the multiple tools are disposed perpendicularly to the wall, however some of them are inclined respectively at an angle β and or an angle −β as explained above in order to provide in-depth treatment of the transition zones 2 h-2 k. FIG. 7 is a side view of a head with a said first shaft of the same robot carriage 3 fitted with two second carriages 4 c that are diametrically opposite carrying two diametrically opposite peening tools 5 with a small offset along the axis XX. FIG. 7A is a face view of a turntable, here carrying four peening tools uniformly distributed around the circumference. Under such circumstances, said tools are preferably disposed in diametrically-opposite pairs, on two transverse guide supports 4 b that are offset by 90°, each supporting two of said second carriages that are radially movable independently of each other, preferably with the two transverse guide supports 4 b being at a small offset in translation along the axis XX. 

1-19. (canceled)
 20. A peening device suitable for peening the insides of undersea pipes made of steel assembled by annular welding of abutting ends of unitary pipe elements, the weld beads being made from the outside of the pipe, said device comprising at least one peening tool suitable for moving in longitudinal axial translation XX in the axial direction of the pipe, and in rotation about said axial longitudinal axis XX of the pipe in the vicinity of said welds inside the pipe, said peening device having at least one hammer comprising: a main body constituting a flyweight of elongate shape in a longitudinal direction Y1Y1 for reciprocating movement in translation of said hammer relative to the peening tool and relative to the inside surface of the pipe and the weld for peening; and a rounded element of curvature of convex shape at the end of said flyweight and secured thereto, said rounded element being suitable for coming into contact with said surface for peening, thereby creating impacts in the form of craters under the effect of the kinetic energy of said hammer when it is actuated for peening by performing said reciprocating movements in translation in the radial direction; wherein: a) said peening tool has a single hammer; and b) said hammer is pivotally mounted so as to be capable of varying the angle of inclination of said elongate flyweight and of varying said direction Y1Y1 of relative reciprocating movement in translation of said hammer relative to the radial direction YY; and wherein c) said device comprises: a first carriage suitable for moving in axial longitudinal translation XX inside a pipe; said first carriage supporting means for moving said peening tool in relative axial longitudinal translation XX relative to said first carriage; said first carriage supporting means for implementing relative rotation of said peening tool relative to said first carriage about said axial longitudinal axis XX of the pipe; and said first carriage supporting means for moving said peening tool in said radial movement YY relative to said first carriage; and d) said peening tool includes means for actuating peening by said radial reciprocating movement in translation by implementing electromagnetic energy, the hammer comprising a said main body made of magnetic material suitable for reciprocating in both directions inside a stationary solenoid coil along the axial direction of said solenoid corresponding to said longitudinal direction Y1Y1 of said hammer under the effect of a magnetic field created inside the solenoid when said solenoid is powered with DC alternately in both directions, said main body also preferably co-operating with a spring.
 21. The device according to claim 20, wherein the electrical power supply of the solenoid is controlled by a digital control circuit enabling the peening energy to be adapted as a function of the position of the hammer as determined by a sensor.
 22. The device according to claim 20, wherein: said first carriage is motor driven and supports a first shaft disposed inside the pipe in said axial longitudinal direction XX of the pipe; and said first shaft supports at least transverse guidance support or means preferably in the form of a beam, suitable for guiding the movement of at least one second carriage in radial translation in a transverse direction perpendicular to said axial longitudinal direction XX, said second carriage supporting said peening tool and said second carriage preferably including means suitable for maintaining said peening tool in a position facing the inside surface of said pipe; said first shaft includes drive means for causing it to perform controlled rotation about its own said axial longitudinal axis XX so as to be capable of moving said radial transverse guide support and said peening tool in relative rotation over the entire circumference of the inside surface of the pipe; and said first shaft is preferably suitable for being driven in relative translation relative to said first carriage in said axial longitudinal direction XX of the pipe, at least over a said limited distance L.
 23. The device according to claim 20, wherein said first carriage is driven by a motor powered from outside the pipe by an umbilical connection, and said first carriage has wheels pressed against the inside surface of the pipe and guiding said axial longitudinal movement in translation of said first carriage inside the pipe, said wheels being connected to an axial main body of the first carriage by a system of arms mounted as hinged parallelograms.
 24. The device according to claim 23, wherein said system of arms mounted as hinged parallelograms comprises three parallelogram structures, each carrying two wheels in alignment on the axial direction XX of the pipe, the three parallelogram structures preferably being distributed uniformly at 120° from one another, and being actuated synchronously by springs or actuators so that the main body of said first carriage remains substantially on the axis XX of said pipe.
 25. The device according to claim 20, wherein said convex element is a body of revolution with section of spherical, oval, or parabolic shape, preferably spherical, made of a steel or metallic carbide of greater hardness than said main body of the hammer, and said convex element presents a small dimension in cross-section, in particular a diameter that is small relative to said main body of the hammer.
 26. The device according to claim 20, having a plurality of peening tools, each comprising a single said hammer, each peening tool being suitable for being moved independently, and each hammer being suitable for being controlled to perform peening independently.
 27. The device according to claim 26, having two peening tools, said first shaft supporting two said second carriages each supporting one said peening tool on a common said transverse guidance support.
 28. The device according to claim 26, having four peening tools, said first shaft supporting two said transverse guidance supports offset in the longitudinal and rotary directions, each of said guidance supports being suitable for guiding the movement of two said second carriages in radial translation, each carriage supporting a single said peening tool.
 29. A method of making undersea steel pipes, the method comprising assembling unit pipe elements by end-to-end butt welding, the weld beads of steel or metal alloy of said welds being disposed on the outside of the pipe, wherein localized peening is performed inside the pipe to increase the compression of the steel or the metal at said welds and on the adjacent peripheral inside surface of the pipe on either side of the welds so as to create a swath of peened surface over a limited distance L in the axial longitudinal direction XX of said pipe, preferably a distance L that is not less than the width of the weld, inside the pipe, plus on either side a width lying in the range 1 mm to 10 mm, said peening being performed by creating a plurality of impacts, preferably in the form of adjacent overlapping craters covering the entire surface of said swath, with a device having at least one peening tool according to claim
 1. 30. The method according to claim 29, wherein the weld comprises a main weld bead outside the pipe and a projection or internal seam of smaller thickness projecting from the inside of the pipe, and said peening is performed at least in the transition zone between the inside surface of said seam at the back of the weld bead and the adjacent inside surface of the pipe, by varying the angle of inclination β of the longitudinal direction Y1Y1 of movement in translation of said hammer relative to said direction YY of movement in radial translation of said second carriage.
 31. The method according to claim 29, wherein material is removed by prior winding or milling of the inside surface of the pipe and of the weld bead over the surface for peening, prior to said peening.
 32. The method according to claim 29, wherein said peening is performed in such a manner as to establish compression or increase compression over a thickness of 0.2 mm to 2 mm in said inside surface of the pipe and of said weld.
 33. The method to claim 29, wherein the limited distance L represents one to three times the thickness of the pipe.
 34. The method according to claim 29, wherein peening is performed in such a manner as to obtain a compression stress greater that 5 MPa, preferably greater than 50 MPa, over the entire peened surface.
 35. The method according to claim 29, wherein: said first carriage is moved in translation inside said pipe in said longitudinal axial direction XX, such that said peening tool is substantially positioned so as to be capable of performing peening in said weld zone and on either side thereof over a said distance L for peening astride said weld in said longitudinal axial direction XX; then said peening tool is moved against or close to the inside surface of the pipe by moving said peening tool in radial translation YY; then said peening tool is moved in rotation about said axial longitudinal axis XX over the circumference of the inside surface of the pipe; and then where appropriate, the peening tool is moved in relative translation in the axial longitudinal direction XX relative to said first carriage so as to perform the peening and compression over the entire peened surface.
 36. The method according to claim 29, comprising the following successive steps: 1) in a workshop on land, assembling the respective ends of at least two unit pipe elements together end-to-end by said welding, in order to form pipe strings; and 2) at sea, on board a laying ship fitted with a J-lay tower, assembling respective ends of said strings together by said welding to form a pipe.
 37. An undersea bottom-to-surface connection pipe comprising unit pipe elements that are assembled end-to-end by welding, wherein at least a portion of the pipe includes zones containing said assembly welds between unit pipe elements in which zones the welding comprises a main weld bead outside the pipe with a projection or internal seam of smaller thickness projecting from the inside of the pipe, and in which zones a swath of the inside surface of the pipe in the vicinity of said welds and on either side thereof is peened over a distance L by a plurality of impacts in the form of adjacent overlapping craters covering the entire surface of said swath, the inside surface of said swath being put into uniform compression so as to eliminate any residual traction stresses due to the welding operation, using the method according to claim
 30. 38. The undersea bottom-to-surface connection pipe according to claim 36, that is a catenary pipe of the SCR type having at least a portion that includes the zone in contact with the bottom and extending over at least 100 m and preferably 200 m above the bottom that has been assembled by a method according to claim
 30. 